CODEWITHSUNDEEP
pythonmultithreadingpython-multithreading
python noob
python noob

Reputation: 21

How does multi-threading work in Python 3.4?

I am just playing around with multi-threading, but I can't seem to get it to work. I have looked at other questions, but none really help me. Here's my code so far:

import threading, time

def hello():
    for i in range(1,5):
        time.sleep(1)
        print("Hello")

def world():
    for i in range(1,5):
        time.sleep(1)
        print("World")

newthread = threading.Thread(hello())
newthread.daemon = True
newthread.start()
otherthread = threading.Thread(world())
otherthread.daemon = True
otherthread.start()
print("end")

I expect to get something like:

Hello
World
Hello
World
Hello
World
Hello
World
end

But instead I get:

Hello
Hello
Hello
Hello
World
World
World
World
end

Upvotes: 1

Views: 1256

Answers (2)

Bi Rico
Bi Rico

Reputation: 25813

You want something like this:

import threading, time

def hello():
    for i in range(1,5):
        time.sleep(1)
        print("Hello")

def world():
    for i in range(1,5):
        time.sleep(1)
        print("World")

newthread = threading.Thread(target=hello)
newthread.start()
otherthread = threading.Thread(target=world)
otherthread.start()

# Just for clarity
newthread.join()
otherthread.join()

print("end")

The joins tell the main thread to wait on the other threads before exiting. If you want the main thread to exit without waiting set demon=True and don't join. The output might surprise you a little bit, it's not as clean as you might expect. For example I got this output:

HelloWorld

World
 Hello
World
 Hello
WorldHello

Upvotes: 1

Alex Hall
Alex Hall

Reputation: 36013

threading.Thread(hello())

You called the function hello and passed the result to Thread, so it executed before the thread object even existed. Pass the plain function object:

threading.Thread(target=hello)

Now the Thread will be responsible for executing the function.

Upvotes: 2

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